Changing the Activity / History default view

The associated activity and history views within a given entity are not customizable and you cannot change their default view settings.
Although this type of DOM manipulation is unsupported, if this is a “must have” requirement you can implement the change with the following js script.

put the code inside the entity onload event.

//Activity scheduledend options 
var ActivityOptions = 
{ 
  All : "All",
  Overdue :"Overdue", 
  Today :"Today", 
  Tomorrow :"Tomorrow", 
  Next7Days :"NextXDays;7", 
  Next30Days :"NextXDays;30", 
  Next90Days :"NextXDays;90", 
  Next6Months :"NextXMonths;6" 
} 

//Activity History actualend options 
var HistoryOptions = 
{ 
  All : "All",
  Today : "Today", 
  Yesterday : "Yesterday", 
  Last7Days : "LastXDays;7", 
  Last30Days : "LastXDays;30", 
  Last90Days : "LastXDays;90", 
  Last6Months : "LastXMonths;6", 
  Last12Months: "LastXMonths;12" 
} 

var _loadarea = loadArea; 
loadArea = function(sArea, sParams, sUrl, bIsvMode) 
{ 
  //load the iframe 
  _loadarea(sArea, sParams, sUrl, bIsvMode); 
  
  if( sArea != "areaActivityHistory" && 
      sArea != "areaActivities" ) return;

  //create the iframe object 
  var iframe = document.getElementById(sArea + "Frame"); 
  //wait until the iframe is fully loaded ("complete") 
  iframe.onreadystatechange = function() 
  { 
    if( iframe.readyState == "complete") 
    { 
      var picklist,option; 
      //reference to the iframe document 
      var iframeDoc = iframe.contentWindow.document; 
      switch(sArea) 
      { 
        case "areaActivityHistory": 
        picklist = iframeDoc.all.actualend[0]; 
        /* change to suit your needs */ 
        option = HistoryOptions.Last90Days; 
        break; 
        case "areaActivities": 
        picklist = iframeDoc.all.scheduledend[0]; 
        /* change to suit your needs */ 
        option = ActivityOptions.Next7Days; 
        break; 
        default: return; 
      } 
      picklist.value = option; 
      picklist.FireOnChange(); 
    } 
  } 
}